Bile salts are substances excreted by the liver which play a key role in the solubilization and transport of dietary fats and other lipidic materials in the upper intestine. This solubilization by micellular aggregates of the bile salts is a direct aid in the absorption of fats, and also in the function of the hydrolytic enzyme, lipase. The major objective of the research project is to study by calorimetric methods the binding of fatty acids, alcohols, and other lipidic materials to the bile salt micelles. Attempts will be made to evaluate binding constants, enthalpies, entropies, and heat capacity changes associated with the binding process. From the thermodynamic information provided by the measurements, the effects of reaction conditions, substrate structural features, and the nature of the bile salt micelles on the stability of the complexes will be generated. Through the use of the model behavior of previously studied, simpler compounds, attempts will be made to explain the binding of fat-derived molecules to the bile salt micelles in forms of hydrophobic or hydrophilic effects. Since a number of pathological conditions associated with various metabolic and digestive diseases are related to the activity of bile salts in the intestine, these studies could provide a basis for understanding these disorders at the molecular level.